This invention relates generally to brake control techniques in motor vehicles, and more particularly to a method for controlling the braking operation in accordance with an instantaneous vehicle speed relative to the ground so that the occurrence of "wheel lock" is prevented and any possibility of causing skidding is eliminated. The invention is further concerned with an electric circuit for simulating the vehicle speed relative to the ground and an apparatus for practicing the aforementioned method.
Heretofore, various methods and apparatuses have been proposed for controlling the braking force in automobiles thereby to prevent wheel lock and minimize braking distance.
In most of the conventional methods or apparatuses, the vehicle speed relative to the ground is first detected, and the braking force is so adjusted that the peripheral speeds of the wheels under braking are maintained at approximately 80% of the vehicle speed. Such a practice has been believed to be specifically advantageous when road conditions and other factors are taken into consideration.
Conventionally, the vehicle speed relative to the ground has been obtained in the manner described below. Trains of pulses representing rotating speeds of the wheels are produced by means of a plurality of sensors provided on the wheel axles of the vehicle; of these pulse trains, one representing the highest wheel speed is selected; and the pulse train thus selected is thereafter corrected so that a corrected signal simulating the vehicle speed relative to ground is obtained, this corrected signal being used for producing a deceleration corresponding to 1.2G. The vehicle speed relative to ground thus simulated will be hereinafter called the "simulated vehicle speed."
According to the conventional systems as described above, it has been difficult to obtain a "simulated vehicle speed" of sufficient accuracy and even when accurate "simulated vehicle speed" is obtained, accurate control of the braking force cannot be attained unless the relation between the slip (s) and the adhesive coefficient (.mu.) of the road surface is taken into consideration.